The 3rd Generation Partnership Program (3GPP) works together with industry to forge mobile telephone standards such as the Long Term Evolution (LTE) phone specification. The LTE specification has developed a discontinuous receive (DRX) mode that can enable some power savings for the mobile handset (often referred to as user equipment or UE). The DRX mode allows the UE to disconnect or “sleep” for periods of time and thereby preserve battery life.
DRX mode was initially envisioned for use when the UE is disconnected from the network (NW), which means that the UE was not actively involved in transferring data between the UE and the NW. Another way to extend battery life is to allow a similar discontinuous receive mode to occur while the UE is connected to the NW. This connected mode discontinuous receive (C-DRX) can allow the UE to sleep, while connected to the NW but not actively transferring data with the NW.
Sometimes, the UE can tune away from an access point (eNodeB, for example) to perform other tasks. If the NW is aware of the tune-away time instances, the NW might configure the UE in C-DRX. When the UE returns to the eNodeB, the NW may be out of sync with the UE. This condition can also be true if the UE has suffered from a signal fade while in C-DRX.
When the UE returns after a long tune away or a long signal fade, the UE needs to indicate to the network that it has returned in order to quickly resume the communication. When the UE returns after having previously been in C-DRX configured by the network, the UE would like, among other desires, to: (1) indicate to the network that the UE has tuned back and to receive a confirmation back from the network, (2) benefit as much as possible from the battery savings of C-DRX, and (3) minimize the latency of the tune back process in case the user equipment has uplink data to send to the network or the network has downlink data to send to the UE.
Therefore, what is desired is a method to take advantage of the UE's C-DRX configuration while still indicating the tune back as quickly as possible.